Compressible pile rheostat



y 26, 1931. v. E. WOODCOCK 7 1,807,366

COMPRESSIBLE PILE RHEOSTAT Filed July 27, 1929 Inventor: Vmgil EWoodcock, b His Atbov'neg.

Patented May 26, 1931 UNITED STATES PATENT OFFICE VIRGIL E. WOODCOCK, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION NEW YORK COMPRESSIBLE PILE RHEOSTAT Application filed July 27, 1s2a.'ser1a1- iwo.- 381,530.

My invention relates to improvements in rheostats of the compressible pile type.

It has long been known that a rheostat may be constructed by utilizing a number of car- 5 bon disks placed one upon the other and that such a rheostat may be used to vary gradually the resistance of a circuit so that the current may be controlled thereby. Such a rheostat has many advantages among which are the smoothness of operation and absence of noises or disturbances in the circuit which arise when a contact finger jumps from one coil to another in the common type of, resistance wire rheostats. There is, however, an. inherent characteristic of a carbon pile rheostat which presents a problem that must be solved if it is to be used advantageously. This is the very rapid variation in resistance which occurs over a comparatively short range of pressure change on the carbon pile.

In the usual applications of the carbon pile rheostat such as the control of the filament current of vacuum tubes, starting resistance for electric motors, or in more specialized fields such as liquid level indicators,

a substantially uniform variation in resistance is generally desirable.

My invention has for one of its objects the provision of a method for applying pressure to the carbon pile so that the resulting variation in resistance is substantially uniform for all increments of the actuating means.

Another object is to provide a carbon disk rheostat pressure applying means which gives a predetermined resistance change for each unit of advance of the actuator.

Another object is to provide a compressible pile rheostat which may be very cheaply manufactured.

Another object of the invention is to provide a carbon disk rheostat which is small, compact and adapted for a variety of uses.

Another object is to provide a compressible fluid within an elastic container to transmit pressure from the actuator to the compressible pile.

Other objects and advantages of my invention will become apparent with a study of the more detailed description set fort hereinafter.

sired resultant pressure for each fraction of I a turn of the actuator, or each fraction of a distance which it progresses, the gas may be enclosed in a suitable elastic container, such as rubber.

Fig. 1 of the drawings represents one embodiment of my invention as applied to a compressible pile rheostat. Fig. 2 illustrates an application of the invention to a starting resistor, while Fig. 3 illustrates the final position in the operation of the apparatus shown in Fig. 2.

. In the drawings, Fig. 1', pressure is applied to the carbon piles 1 by means of a. yoke 5 which is moved in a forward direction by means of the actuating screw 6, the yoke pressing against gas filled elastic spheroids which in turn bear against a plate 3 which serves to apply pressure upon the carbon piles and to connect the two piles. This plate normally is held away from the carbon piles by means of springs 2.

Rigid cylindrical members 9 serve to limit the amount of expansion of the flexible gas containers. As the yoke progresses, decreasing the volume of gas the elastic container will press against the walls of member 9 and thereafter a greater pressure will be applied to the carbon pile per unit advance of the yoke 5. The material used for member 9 is unimportant; it may be iron, wood, or a woven net or other inelastic material. The carbon piles may be supported by any suitable means within the casing and a knob 8 may be provided for the easy actuation of the operating screw 6, although these may be varied to suit the application of the resistor.

It will be apparent that the pressure applied to the compressible pile for each unit of advance of the yoke will depend upon the thickness of the container, the kind of compressible fluid with which it is filled, the initial pressure of the inflated container,

- applied through the outer and the shape of the member surrounding the flexible bags.

It follows that the resulting pressure applied to. the compressible pile may be predetermined so as to produce any desired resistance change by varying the factors named. A straight line variation maybe readily obtained by suitably proportlonmg these parts against the characteristics of the selected compressible pile.

In Fig. 2, the invention is illustratedm application to a starting resistance in whlch 10 represents a member which applies pres sure to the carbon pile 1, through the interposed inflated elastic container 11 or spheroid, as the member 10 is advanced the inflated elastic container 11 is flattened out; it is pressure expansible, the material being stretched; the volume changes; the pressure upon the container changes; and the result ant pressure against the carbon pile also changes as the member 10 continues to ad- Vance. The rate of change of pressure applied to. the pile will depend on the initial pressure of the inflated container, the shape and elasticity of said container. and the rate at which member 10 progresses.

In Fig. 3, the member 10 is shown enclosing the elastic container so that after a pressure has been applied which is great enough to flatten out the container, it will rest with-' in member 10 and further pressure may be edges of the concave member 10. The provision of a member so formed makes it possible to apply pressure to the compressible pile directly after the inherent resistance characteristic of the pile has been compensated for by the interposed elastic container so that a minimum of resistance is left in the circuit due to said pile. This provision relieves the inflated container from the burden of carryin the greater pressures.

t is to be understood that I have described what is believed. to be the best embodiment of myinvention but I am not to be limited in any way to the exact disclosure described and what I believe to be new and novel I will now point out more particularly in the ap ended claims.

What claim as new and desire to secure by Letters Patent of the United States, is:

1. A compressible pile rheostat which consists of two comlpressible piles, an inflated elastic pressure ag for each, an inelastic member with its axls parallel to the axis of said piles surrounding each bag, a yoke for applying pressure simultaneously to said ags, and an actuating means for the yoke adapted to move said yoke against said bags to apply pressure to said compressible piles.

2. A pressure applying device for a compressible pile rhcostat, including an inflated elastic container, a concave member adapted to compress said container, actuating means ber adapted to apply pressure thereto, said.

member having a recess in which said container may rest.

4. A pressure applying device for a compressible pile resistor including a sealed elastic container and means for applying pres sure to said pressure pile resistor through said container and thereafter applying pres sure directly.

5. As an article of manufacture, a pressure applying device for a compressible pile reslstor comprising a spheroid of elastic pressure-expansible material.

6. In a pressure applying device, pressure applying means therefor and a spheroid of elastlc pressure-expansible material interposed between said p-ressure means and said pile whereby pressure is applied on said container expanding the same over all of its unconfined area, the container transmitting a fraction of said pressure to said pile.

7. A rheostat comprising one or more compressible piles, gas inflated containers therefor formed of material which may be stretched, means for applying pressure on said containers distending the same and thence to said piles, whereby only a fraction of said pressure is transmitted to said piles.

8. In a compressible pile rheostat the combination of a compressible pile, pressure applying means therefor, and an inflated elastic container interposed between said pressure means and said pile whereby pressure is applied upon said container expanding the same, the container transmitting a fraction of said pressure to said pile and means for limiting the expansion of said container.

In Witness whereof, I have hereunto set my hand this 25th day of July, 1929.

VIRGIL E. WOODCOCK. 

